Patterning process and resist composition

ABSTRACT

A negative pattern is formed by coating a resist composition comprising a polymer comprising recurring units having a carboxyl group substituted with an acid labile group of tertiary ester and an optional acid generator onto a substrate, prebaking, exposing to high-energy radiation, baking, and developing in an organic solvent developer so that the unexposed region of resist film is dissolved away and the exposed region of resist film is not dissolved. The resist composition exhibits a high dissolution contrast during organic solvent development and forms a fine hole or trench pattern at a high sensitivity and dimensional control.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a)on Patent Application No. 2012-137942 filed in Japan on Jun. 19, 2012,the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a pattern forming process involving exposureof resist film, deprotection reaction with the aid of acid and heat, anddevelopment in an organic solvent to form a negative tone pattern inwhich the unexposed region is dissolved and the exposed region is notdissolved. It also relates to a resist composition used therein.

BACKGROUND ART

Among the current lithography processes, the process of recent interestis a double patterning process involving a first set of exposure anddevelopment to form a first pattern and a second set of exposure anddevelopment to form a pattern between the first pattern features. Anumber of double patterning processes are proposed. One exemplaryprocess involves a first set of exposure and development to form aphotoresist pattern having lines and spaces at intervals of 1:3,processing the underlying layer of hard mask by dry etching, applyinganother layer of hard mask thereon, a second set of exposure anddevelopment of a photoresist film to form a line pattern in the spacesof the first exposure, and processing the hard mask by dry etching,thereby forming a line-and-space pattern at a half pitch of the firstpattern.

An alternative process involves a first set of exposure and developmentto form a photoresist pattern having spaces and lines at intervals of1:3, processing the underlying layer of hard mask by dry etching,applying a photoresist layer thereon, a second set of exposure anddevelopment to form a second space pattern on the remaining hard maskportion, and processing the hard mask by dry etching. In either process,the hard mask is processed by two dry etchings.

As compared with the line pattern, the hole pattern is difficult toreduce the feature size. In order for the prior art method to form fineholes, an attempt is made to form fine holes by under-exposure of apositive resist film combined with a hole pattern mask. This, however,results in the exposure margin being extremely narrowed. It is thenproposed to form holes of greater size, followed by thermal flow orRELACS® method to shrink the holes as developed. However, there is aproblem that control accuracy becomes lower as the pattern size afterdevelopment and the size after shrinkage differ greater and the quantityof shrinkage is greater. With the hole shrinking method, the hole sizecan be shrunk, but the pitch cannot be narrowed.

It is then proposed in Non-Patent Document 1 that a pattern ofX-direction lines is formed in a positive resist film using dipoleillumination, the resist pattern is cured, another resist material iscoated thereon, and a pattern of Y-direction lines is formed in theother resist film using dipole illumination, leaving a grid linepattern, spaces of which provide a hole pattern. Although a hole patterncan be formed at a wide margin by combining X and Y lines and usingdipole illumination featuring a high contrast, it is difficult to etchvertically staged line patterns at a high dimensional accuracy. It isproposed in Non-Patent Document 2 to form a hole pattern by exposure ofa negative resist film through a Levenson phase shift mask ofX-direction lines combined with a Levenson phase shift mask ofY-direction lines. However, the crosslinking negative resist film hasthe drawback that the resolving power is low as compared with thepositive resist film, because the maximum resolution of ultrafine holesis determined by the bridge margin.

A hole pattern resulting from a combination of two exposures of X- andY-direction lines and subsequent image reversal into a negative patterncan be formed using a high-contrast line pattern of light. Thus holeshaving a narrow pitch and fine size can be opened as compared with theprior art.

Non-Patent Document 3 reports three methods for forming hole patternsvia image reversal. The three methods are: method (1) involvingsubjecting a positive resist composition to two double-dipole exposuresof X and Y lines to form a dot pattern, depositing a SiO₂ film thereonby LPCVD, and effecting O₂-RIE for reversal of dots into holes; method(2) involving forming a dot pattern by the same steps as in (1), butusing a resist composition designed to turn alkali-soluble andsolvent-insoluble upon heating, coating a phenol-base overcoat filmthereon, effecting alkaline development for image reversal to form ahole pattern; and method (3) involving double dipole exposure of apositive resist composition and organic solvent development for imagereversal to form holes.

The organic solvent development to form a negative pattern is atraditional technique. A resist composition comprising cyclized rubberis developed using an alkene such as xylene as the developer. An earlychemically amplified resist composition comprisingpoly(tert-butoxycarbonyloxystyrene) is developed with anisole as thedeveloper to form a negative pattern.

Recently a highlight is put on the organic solvent development again. Itwould be desirable if a very fine hole pattern, which is not achievablewith the positive tone, is resolvable through negative tone exposure. Tothis end, a positive resist composition featuring a high resolution issubjected to organic solvent development to form a negative pattern. Anattempt to double a resolution by combining two developments, alkalinedevelopment and organic solvent development is under study.

As the ArF resist composition for negative tone development with organicsolvent, positive ArF resist compositions of the prior art design may beused. Such pattern forming processes are described in Patent Documents 1to 3. These patent documents disclose resist compositions for organicsolvent development comprising a copolymer of hydroxyadamantanemethacrylate, a copolymer of norbornane lactone methacrylate, and acopolymer of methacrylate having acidic groups including carboxyl,sulfo, phenol and thiol groups substituted with two or more acid labilegroups, and pattern forming processes using the same.

Further, Patent Document 4 discloses a process for forming a patternthrough organic solvent development in which a protective film isapplied onto a resist film. Patent Document 5 discloses a topcoatlessprocess for forming a pattern through organic solvent development inwhich an additive is added to a resist composition so that the additivemay segregate at the resist film surface after spin coating to providethe surface with improved water repellency.

In positive development wherein a carboxyl group is generated bydeprotection reaction and a dissolution rate is increased byneutralization reaction with aqueous alkaline developer, the dissolutionrate of exposed region is at least 1,000 times higher than thedissolution rate of unexposed region, indicating a high dissolutioncontrast. By contrast, in negative development via organic solventdevelopment, the dissolution rate of unexposed region due to solvationis slow and therefore, the dissolution rate differs by a factor of lessthan 100 between unexposed and exposed regions. A new resist materialmust be sought for before the dissolution contrast of negativedevelopment via organic solvent development can be enhanced.

CITATION LIST

-   Patent Document 1: JP-A 2008-281974-   Patent Document 2: JP-A 2008-281975-   Patent Document 3: JP 4554665-   Patent Document 4: JP 4590431-   Patent Document 5: JP-A 2008-309879-   Non-Patent Document 1: Proc. SPIE Vol. 5377, p. 255 (2004)-   Non-Patent Document 2: IEEE IEDM Tech. Digest 61 (1996)-   Non-Patent Document 3: Proc. SPIE Vol. 7274, p. 72740N (2009)

DISCLOSURE OF INVENTION

The organic solvent development is low in dissolution contrast, ascompared with the positive resist system adapted to be dissolved inalkaline developer when deprotection reaction takes place to produceacidic carboxyl or phenolic groups. Specifically, on development inaqueous alkaline developer, the dissolution rate differs more than 1,000times between unexposed and exposed regions, whereas the differenceassociated with organic solvent development is only about 100 times, andeven about 10 times in the case of certain materials. With such smalldifferential dissolution, no sufficient margin is available. In the caseof aqueous alkaline development, the dissolution rate is improved byneutralization reaction with carboxyl groups. In the case of organicsolvent development with no accompanying reaction, the dissolution rateis low because dissolution is solely due to solvation. It is necessarynot only to increase the dissolution rate of the unexposed region, butalso to minimize the dissolution rate of the exposed region where theresist film is to be retained. If the dissolution rate of the exposedregion is high, the thickness of the remaining film is so reduced thatthe underlying substrate may not be processed by subsequent etchingthrough the pattern as developed. Further it is important to enhance thegradient or gamma (γ) at the dose corresponding todissolution/non-dissolution conversion. A low γ value is prone to forman inversely tapered profile and allows for pattern collapse in the caseof a line pattern. To obtain a perpendicular pattern, the resist musthave a dissolution contrast having a γ value as high as possible.

While prior art photoresist compositions of the aqueous alkalinesolution development type are described in Patent Documents 1 to 3, theyhave a low dissolution contrast upon organic solvent development. Itwould be desirable to have a novel material having a significantdifference in dissolution rate between the exposed and unexposed regionsand capable of achieving a high dissolution contrast (γ) upon organicsolvent development.

When an attempt is made to form a hole pattern through negativedevelopment, regions surrounding the holes receive light so that excessacid is generated therein. Since the holes are not opened if the aciddiffuses inside the holes, control of acid diffusion is also important.

An object of the invention is to provide a resist composition which hasa significant dissolution contrast and a high sensitivity upon organicsolvent development. Another object is to provide a pattern formingprocess capable of forming a hole or trench pattern viapositive/negative reversal by organic solvent development.

The inventors have found that a polymer comprising recurring unitssubstituted with an acid labile group of tertiary ester type such asisopropyl, tert-butyl or tert-amyl which is attached to a ring iseffective, and that a resist composition comprising the polymer as baseresin is improved in dissolution contrast upon organic solventdevelopment following exposure and PEB.

When such an acid labile group is applied to a positive resist film foralkaline development, problems like pattern collapse and bridgingbetween pattern features arise due to swell in developer becausebranched alkyl group is highly lipophilic. When the same acid labilegroup is applied to negative pattern formation via organic solventdevelopment, a high dissolution contrast is available because ofimproved developer solubility of branched alkyl group. Neither patterncollapse nor bridging between pattern features arises because of noswell in organic solvent developer.

Another means of improving the solubility in organic solvent developeris by introducing fluorine into an acid labile group as described inJP-A 2012-008500 (WO 2012/002519). Since fluorinated alkyl groups aresignificantly improved in lipophilicity, solubility in developer isimproved. However, since an acid labile group of tertiary ester typehaving fluorine introduced therein requires a very large amount ofactivation energy for deprotection, the PEB temperature must be elevatedso that the PEB temperature margin is reduced, and to in some cases,deprotection reaction itself does not take place. By contrast, the acidlabile group having formula (1) is devoid of such disadvantages since itis free of fluorine.

Accordingly, in one aspect, the invention provides a pattern formingprocess comprising the steps of applying a resist composition comprisinga polymer and an optional acid generator onto a substrate, prebaking thecomposition to form a resist film, exposing the resist film tohigh-energy radiation, baking, and developing the exposed film in anorganic solvent-based developer to form a negative pattern wherein theunexposed region of film is dissolved away and the exposed region offilm is not dissolved. The polymer comprises recurring units having acarboxyl group whose hydrogen is substituted by an acid labile grouphaving the general formula (1).

Herein R¹ is a straight, branched or cyclic C₁-C₇ alkyl group, R², R³and R⁴ each are hydrogen, methyl or ethyl, excluding the event that atleast two of R², R³ and R⁴ are hydrogen, R⁵ is hydrogen or methyl, andR⁶ is methylene or ethylene.

In a preferred embodiment, the recurring units having a carboxyl groupsubstituted with an acid labile group are units (a1) having the generalformula (2).

Herein R⁷ is hydrogen or methyl, R⁸ is an acid labile group havingformula (1), X¹ is a single bond, phenylene, naphthylene, or—C(═O)—O—R⁹—, R⁹ is a straight, branched or cyclic C₁-C₁₀ alkylene groupwhich may contain an ether radical, ester radical, lactone ring orhydroxyl radical, or phenylene or naphthylene group, and 0<a1<1.0.

In a preferred embodiment, the polymer may further comprise recurringunits of at least one type selected from recurring units (a2) having thegeneral formula (3) and recurring units (b1) to (b4) having the generalformula (4).

Herein R¹⁰ is hydrogen or methyl, R¹¹ is an acid labile group differentfrom formula (1), X² is a single bond, phenylene, naphthylene or—C(═O)—O—R¹²—, R¹² is a straight, branched or cyclic C₁-C₁₀ alkylenegroup which may contain an ether radical, ester radical, lactone ring orhydroxyl radical, or phenylene or naphthylene group, and 0≦a2<1.0.

Herein R¹³ and R¹⁶ each are hydrogen or methyl, R¹⁴ is a straight,branched or cyclic, di- to penta-valent C₁-C₁₆ aliphatic hydrocarbongroup which may contain an ether or ester radical, R¹⁵ and R¹⁷ each arean acid labile group, R¹⁸ to R²¹ and R²² to R²⁵ are each independentlyhydrogen, cyano, a straight, branched or cyclic C₁-C₆ alkyl group,alkoxycarbonyl group, or ether or lactone ring-containing group, atleast one of R¹⁸ to R²¹ and R²² to R²⁵ has an acid labilegroup-substituted hydroxyl group, m is an integer of 1 to 4, n is 0 or1, b1, b2, b3 and b4 are in the range: 0≦b1<1.0, 0≦b2<1.0, 0≦b3<1.0,0≦b4<1.0, 0≦b1+b2+b3+b4<1.0, and 0<a2+b1+b2+b3+b4<1.0.

In a preferred embodiment, the polymer may further comprise recurringunits derived from a monomer having an adhesive group selected from theclass consisting of hydroxyl, cyano, carbonyl, ester, ether, lactonering, carboxyl, carboxylic anhydride, sulfonic acid ester, disulfone,and carbonate.

In a preferred embodiment, the polymer may further comprise recurringunits (d1), (d2) or (d3) having the following general formula.

Herein R⁰²⁰, R⁰²⁴ and R⁰²⁸ each are hydrogen or methyl, R⁰²¹ is a singlebond, phenylene, —O—R⁰³³—, or —C(═O)—Y—R⁰³³—, Y is oxygen or NH, R⁰³³ isa straight, branched or cyclic C₁-C₆ alkylene group, alkenylene orphenylene group, which may contain a carbonyl (—CO—), ester (—COO—),ether (—O—) or hydroxyl radical, R⁰²², R⁰²³, R⁰²⁵, R⁰²⁶, R⁰²⁷, R⁰²⁹,R⁰³⁰, and R⁰³¹ are each independently a straight, branched or cyclicC₁-C₁₂ alkyl group which may contain a carbonyl, ester or ether radical,or a C₆-C₁₂ aryl, C₇-C₂₀ aralkyl, or thiophenyl group, Z¹ is a singlebond, methylene, ethylene, phenylene, fluorophenylene, —O—R⁰³²—, or—C(═O)—Z²—R⁰³²—, Z² is oxygen or NH, R⁰³² is a straight, branched orcyclic C₁-C₆ alkylene group, alkenylene or phenylene group, which maycontain a carbonyl, ester, ether or hydroxyl radical, M⁻ is anon-nucleophilic counter ion, d1, d2 and d3 are in the range: 0≦d1≦0.3,0≦d2≦0.3, 0≦d3≦0.3, 0≦d1+d2+d3≦0.3.

Typically, the developer comprises 2-octanone, 2-nonanone, 2-heptanone,3-heptanone, 4-heptanone, 2-hexanone, 3-hexanone, diisobutyl ketone,methylcyclohexanone, acetophenone, methylacetophenone, propyl acetate,butyl acetate, isobutyl acetate, amyl acetate, isoamyl acetate, butenylacetate, propyl formate, butyl formate, isobutyl formate, amyl formate,isoamyl formate, methyl valerate, methyl pentenoate, methyl crotonate,ethyl crotonate, methyl propionate, ethyl propionate, ethyl3-ethoxypropionate, methyl lactate, ethyl lactate, propyl lactate, butyllactate, isobutyl lactate, amyl lactate, isoamyl lactate, methyl2-hydroxyisobutyrate, ethyl 2-hydroxyisobutyrate, methyl benzoate, ethylbenzoate, phenyl acetate, benzyl acetate, methyl phenylacetate, benzylformate, phenylethyl formate, methyl 3-phenylpropionate, benzylpropionate, ethyl phenylacetate, 2-phenylethyl acetate, or a mixture oftwo or more of the foregoing.

In a preferred embodiment, the step of exposing the resist film tohigh-energy radiation includes KrF excimer laser lithography ofwavelength 248 nm, ArF excimer laser lithography of wavelength 193 nm,EUV lithography of wavelength 13.5 nm or EB lithography.

In another embodiment, the pattern forming process is modified ascomprising the steps of applying a resist composition onto a substrate,the resist composition comprising a polymer comprising recurring unitshaving a carboxyl group which is substituted with an acid labile grouphaving formula (1), an optional acid generator, and an organic solvent,prebaking the composition to form a resist film, forming a protectivefilm on the resist film, exposing the resist film to high-energyradiation, baking, and applying an organic solvent-based developer todissolve away the protective film and the unexposed region of resistfilm for forming a negative pattern wherein the exposed region of resistfilm is not dissolved.

In a second aspect, the invention provides a negative pattern-formingresist composition comprising a polymer, an acid generator, and anorganic solvent. The polymer comprises recurring units (a1) having acarboxyl group which is substituted with an acid labile group having theabove formula (1), the units (a1) having the above formula (2) and isdissolvable in a developer selected from the same solvents as listedabove.

Preferably, the polymer may further comprise recurring units of at leastone type selected from recurring units (a2) having the above formula (3)and recurring units (b1) to (b4) having the above formula (4); recurringunits derived from a monomer having an adhesive group selected from theclass consisting of hydroxyl, cyano, carbonyl, ester, ether, lactonering, carboxyl, carboxylic anhydride, sulfonic acid ester, disulfone,and carbonate; and/or recurring units (d1), (d2) or (d3) having theabove formula.

ADVANTAGEOUS EFFECTS OF INVENTION

A resist composition comprising as base resin a polymer comprisingrecurring units substituted with an acid labile group of tertiary estertype such as isopropyl, tert-butyl or tert-amyl which is attached to aring offers a very high dissolution contrast upon organic solventdevelopment following exposure and PEB. When the resist film is exposedimagewise and developed in an organic solvent, a fine hole or trenchpattern can be formed at a high sensitivity and dimensional controlaccuracy.

BRIEF DESCRIPTION OF DRAWINGS

The only FIGURE, FIG. 1 is a cross-sectional view of a patterningprocess according to one embodiment of the invention. FIG. 1A shows aphotoresist film disposed on a substrate, FIG. 1B shows the resist filmbeing exposed, and FIG. 1C shows the resist film being developed in anorganic solvent.

DESCRIPTION OF EMBODIMENTS

The terms “a” and “an” herein do not denote a limitation of quantity,but rather denote the presence of at least one of the referenced item.“Optional” or “optionally” means that the subsequently described eventor circumstances may or may not occur, and that description includesinstances where the event or circumstance occurs and instances where itdoes not. As used herein, the notation (C_(n)-C_(m)) means a groupcontaining from n to m carbon atoms per group. As used herein, the term“film” is used interchangeably with “coating” or “layer.” The term“processable layer” is interchangeable with patternable layer and refersto a layer that can be processed such as by etching to form a patterntherein.

The abbreviations and acronyms have the following meaning.

Mw: weight average molecular weight

Mn: number average molecular weight

Mw/Mn: molecular weight distribution or dispersity

GPC: gel permeation chromatography

PEB: post-exposure bake

PAG: photoacid generator

Briefly stated, the invention pertains to a process for forming apattern by applying a resist composition comprising a polymer orhigh-molecular-weight compound comprising recurring units substitutedwith an acid labile group of tertiary ester type having isopropyl,tert-butyl or tert-amyl on a ring as base resin and a solvent onto asubstrate, prebaking the composition to remove the unnecessary solventand form a resist film, exposing the resist film to high-energyradiation, PEB, and developing the exposed film in an organicsolvent-based developer to form a negative pattern. The invention alsoprovides the resist composition used herein.

For the purpose of increasing the dissolution rate of the unexposedregion during organic solvent development, it is effective to introducean acid labile group in the form of an alkyl group having many branchedstructures. Solvation progresses in the branched moiety, leading to animprovement in dissolution rate. On the other hand, the acid labilegroup having cyclic structure is effective for preventing aciddiffusion.

When the acid labile group of tertiary ester type having isopropyl,tert-butyl or tert-amyl attached to a ring is introduced, solventsolubility is improved over the acid labile group of tertiary ester typefree of isopropyl, tert-butyl or tert-amyl within a ring. On the otherhand, the cyclic structure functions to prevent acid diffusion. Anegative pattern of organic solvent type featuring low diffusion andhigh contrast can be formed.

Herein the polymer is defined as comprising recurring units having acarboxyl group whose hydrogen is substituted by an acid labile grouphaving isopropyl, tert-butyl, tert-amyl or the like attached to a ring.The acid labile group has the general formula (1).

Herein R¹ is a straight, branched or cyclic C₁-C₇ alkyl group. R², R³and R⁴ each are hydrogen, methyl or ethyl. It is excluded that at leasttwo of R², R³ and R⁴ are hydrogen. R⁵ is hydrogen or methyl. R⁶ ismethylene or ethylene.

Examples of the acid labile group having formula (1) are given below,but not limited thereto.

The recurring units having an acid labile group of tertiary ester typehaving isopropyl, tert-butyl, tert-amyl or the like attached to a ring,as represented by formula (1) are preferably recurring units (a1) havingthe general formula (2).

Herein R⁷ is hydrogen or methyl. R⁸ is an acid labile group havingformula (1). X¹ is a single bond, phenylene, naphthylene, or—C(═O)—O—R⁹—, wherein R⁹ is a straight, branched or cyclic C₁-C₁₀alkylene group which may contain an ether radical, ester radical,lactone ring or hydroxyl radical, or phenylene or naphthylene group, and0<a1<1.0.

Suitable monomers Ma1 from which recurring units (a1) are derived havethe following formula.

Herein R⁷, R⁹ and X¹ are as defined above.

Examples of the monomer Mal wherein X¹ is a variant are given below.

In addition to the recurring units (a1), the polymer may furthercomprise recurring units substituted with an acid labile group otherthan the acid labile group of formula (1), specifically recurring units(a2) having the general formula (3).

Herein R¹⁰ is hydrogen or methyl, R¹¹ is an acid labile group differentfrom formula (1), X² is a single bond, phenylene, naphthylene or—C(═O)—O—R¹²—, wherein R¹² is a straight, branched or cyclic C₁-C₁₀alkylene group which may contain an ether radical, ester radical,lactone ring or hydroxyl radical, or phenylene or naphthylene group, and0≦a2<1.0.

Examples of X² are as exemplified for X¹. The acid labile group R¹¹ willbe described later.

In addition to the recurring units (a1) having formula (2) and recurringunits (a2) having formula (3), the polymer may have furthercopolymerized therein recurring units having a hydroxyl groupsubstituted with an acid labile group. The recurring units having ahydroxyl group substituted with an acid labile group include recurringunits (b1) to (b4) having the general formula (4).

Herein R¹³ and R¹⁶ each are hydrogen or methyl. R¹⁴ is a straight,branched or cyclic, di- to penta-valent C₁-C₁₆ aliphatic hydrocarbongroup which may contain an ether or ester radical. R¹⁵ and R¹⁷ each arean acid labile group. R¹⁸ to R²¹ and R²² to R³⁵ are each independentlyhydrogen, cyano, a straight, branched or cyclic C₁-C₆ alkyl group,alkoxycarbonyl group, or ether or lactone ring-containing group, atleast one of R¹⁸ to R²¹ and R²² to R²⁵ has an acid labilegroup-substituted hydroxyl group. The subscript m is an integer of 1 to4, n is 0 or 1, b1, b2, b3 and b4 are in the range: 0≦b1<1.0, 0≦b2<1.0,0≦b3<1.0, 0≦b4<1.0, 0≦b1+b2+b3+b4<1.0.

Examples of suitable monomers from which recurring units (b1) and (b2)in formula (4) are derived are shown below. Herein R¹³, R¹⁵, R¹⁶ and R¹⁷are as defined above.

Examples of suitable monomers from which recurring units (b3) and (b4)in formula (4) are derived are shown below. Herein R is an acid labilegroup.

The acid labile group R¹¹ (different from formula (1)) substituting onthe carboxyl group in formula (3), and the acid labile groups R¹⁵, R¹⁷,any one of R¹⁸ to R²¹, and any one of R²² to R²⁵ substituting on thehydroxyl group in formula (4) may be selected from a variety of suchgroups and may be the same or different. Suitable acid labile groupsinclude groups of the formula (AL-10), acetal groups of the formula(AL-11), tertiary alkyl groups of the formula (AL-12), and oxoalkylgroups of 4 to 20 carbon atoms, but are not limited thereto.

In formulae (AL-10) and (AL-11), R⁵¹ and R⁵⁴ each are a monovalenthydrocarbon group, typically straight, branched or cyclic alkyl group,of 1 to 40 carbon atoms, more specifically 1 to 20 carbon atoms, whichmay contain a heteroatom such as oxygen, sulfur, nitrogen or fluorine.R⁵² and R⁵³ each are hydrogen or a monovalent hydrocarbon group,typically straight, branched or cyclic alkyl group, of 1 to 20 carbonatoms which may contain a heteroatom such as oxygen, sulfur, nitrogen orfluorine. The subscript “a5” is an integer of 0 to 10, and especially 1to 5. Alternatively, a pair of R⁵² and R⁵³, R⁵² and R⁵⁴, or R⁵³ and R⁵⁴may bond together to form a ring, specifically aliphatic ring, with thecarbon atom or the carbon and oxygen atoms to which they are attached,the ring having 3 to 20 carbon atoms, especially 4 to 16 carbon atoms.

In formula (AL-12), R⁵⁵, R⁵⁶ and R⁵⁷ each are a monovalent hydrocarbongroup, typically straight, branched or cyclic alkyl group, of 1 to 20carbon atoms which may contain a heteroatom such as oxygen, sulfur,nitrogen or fluorine. Alternatively, a pair of R⁵⁵ and R⁵⁶, R⁵⁶ and R⁵⁷,or R⁵⁶ and R⁵⁷ may bond together to form a ring, specifically aliphaticring, with the carbon atom to which they are attached, the ring having 3to 20 carbon atoms, especially 4 to 16 carbon atoms.

Illustrative examples of the group of formula (AL-10) includetert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-amyloxycarbonyl,tert-amyloxycarbonylmethyl, 1-ethoxyethoxycarbonylmethyl,2-tetrahydropyranyloxycarbonylmethyl and2-tetrahydrofuranyloxycarbonylmethyl as well as substituent groups ofthe following formulae (AL-10)-1 to (AL-10)-10.

In formulae (AL-10)-1 to (AL-10)-10, R⁵⁸ is each independently astraight, branched or cyclic C₁-C₈ alkyl group, C₆-C₂₀ aryl group orC₇-C₂₀ aralkyl group. R⁵⁹ is hydrogen or a straight, branched or cyclicC₁-C₂₀ alkyl group. R⁶⁰ is a C₆-C₂₀ aryl group or C₇-C₂₀ aralkyl group;and a5 is an integer of 0 to 10, especially 1 to 5.

Illustrative examples of the acetal group of formula (AL-11) includethose of the following formulae (AL-11)-1 to (AL-11)-112.

Other examples of acid labile groups include those of the followingformula (AL-11a) or (AL-11b) while the polymer may be crosslinked withinthe molecule or between molecules with these acid labile groups.

Herein R⁶¹ and R⁶² each are hydrogen or a straight, branched or cyclicC₁-C₈ alkyl group, or R⁶¹ and R⁶² may bond together to form a ring withthe carbon atom to which they are attached, and R⁶¹ and R⁶² are straightor branched C₁-C₈ alkylene groups when they form a ring. R⁶³ is astraight, branched or cyclic C₁-C₃ alkylene group. Each of b5 and d5 is0 or an integer of 1 to 10, preferably 0 or an integer of 1 to 5, and c5is an integer of 1 to 7. “A” is a (c5+1)-valent aliphatic or alicyclicsaturated hydrocarbon group, aromatic hydrocarbon group or heterocyclicgroup having 1 to 50 carbon atoms, which may be separated by aheteroatom such as oxygen, sulfur or nitrogen or in which some hydrogenatoms attached to carbon atoms may be substituted by hydroxyl, carboxyl,carbonyl radicals or fluorine atoms. “B” is —CO—O—, —NHCO—O— or—NHCONH—.

Preferably, “A” is selected from divalent to tetravalent, straight,branched or cyclic C₁-C₂₀ alkylene, alkanetriyl and alkanetetraylgroups, and C₆-C₃₀ arylene groups, which may be separated by aheteroatom such as oxygen, sulfur or nitrogen or in which some hydrogenatoms attached to carbon atoms may be substituted by hydroxyl, carboxyl,acyl radicals or halogen atoms. The subscript c5 is preferably aninteger of 1 to 3.

The crosslinking acetal groups of formulae (AL-11a) and (AL-11b) areexemplified by the following formulae (AL-11)-113 through (AL-11)-120.

Illustrative examples of the tertiary alkyl group of formula (AL-12)include tert-butyl, triethylcarbyl, 1-ethylnorbornyl,1-methylcyclohexyl, 1-ethylcyclopentyl, and tert-amyl groups as well asthose of (AL-12)-1 to (AL-12)-16.

Herein R⁶⁴ is each independently a straight, branched or cyclic C₁-C₈alkyl group, C₆-C₂₀ aryl group or C₇-C₂₀ aralkyl group, or two R⁶⁴groups may bond together to form a ring with the carbon atom to whichthey are attached, the ring being of 3 to 20 carbon atoms, specifically4 to 16 carbon atoms, typically aliphatic ring. R⁶⁵ and R⁶⁷ each arehydrogen, methyl or ethyl. R⁶⁶ is a C₆-C₂₀ aryl group or C₇-C₂₀ aralkylgroup.

With acid labile groups containing R⁶⁸ representative of a di- orpoly-valent alkylene or arylene group as shown by formula (AL-12)-17,the polymer may be crosslinked within the molecule or between molecules.In formula (AL-12)-17, R⁶⁴ is as defined above, R⁶⁸ is a single bond, astraight, branched or cyclic C₁-C₂₀ alkylene group or arylene group,which may contain a heteroatom such as oxygen, sulfur or nitrogen, andb6 is an integer of 0 to 3. It is noted that formula (AL-12)-17 isapplicable to all the acid labile groups mentioned above.

The groups represented by R⁶⁴, R⁶⁵, R⁶⁶ and R⁶⁷ may contain a heteroatomsuch as oxygen, nitrogen or sulfur. Such groups are exemplified by thoseof the following formulae (AL-13)-1 to (AL-13)-7.

While the polymer used as the base resin in the resist compositioncomprises essentially recurring units (a1) having formula (2) andoptionally (and preferably) recurring units (a2) having formula (3) andacid labile group-bearing recurring units (b1) to (b4) having formula(4), it may have further copolymerized therein recurring units (c)derived from monomers having an adhesive group such as hydroxyl, cyano,carbonyl, ester, ether, lactone ring, carboxyl, carboxylic anhydride,sulfonic acid ester, disulfone or carbonate group. Of these, recurringunits having lactone ring as the adhesive group are most preferred.

Examples of suitable monomers from which recurring units (c) are derivedare given below.

In a preferred embodiment, the polymer has further copolymerized thereinunits selected from sulfonium salt units (d1) to (d3) represented by thegeneral formula below.

Herein R⁰²⁰, R⁰²⁴, and R⁰²⁸ each are hydrogen or methyl. R⁰²¹ is asingle bond, phenylene, —O—R⁰³³—, or —C(═O)—Y—R⁰³³— wherein Y is oxygenor NH and R⁰³³ is a straight, branched or cyclic C₁-C₆ alkylene group,alkenylene group or phenylene group, which may contain a carbonyl(—CO—), ester (—COO—), ether (—O—), or hydroxyl moiety. R⁰²², R⁰²³,R⁰²⁵, R⁰²⁶, R⁰²⁷, R⁰²⁹, R⁰³⁰, and R⁰³¹ are each independently astraight, branched or cyclic C₁-C₁₂ alkyl group which may contain acarbonyl, ester or ether moiety, a C₉-C₁₂ aryl group, a C₇-C₂₀ aralkylgroup, or a thiophenyl group. Z¹ is a single bond, methylene, ethylene,phenylene, fluorinated phenylene, —O—R⁰³²—, or —C(═O)—Z²—R⁰³²—, whereinZ² is oxygen or NH, and R⁰³² is a straight, branched or cyclic C₁-C₆alkylene group, alkenylene group or phenylene group, which may contain acarbonyl, ester, ether or hydroxyl moiety. M⁻ is a non-nucleophiliccounter ion. Molar fractions d1, d2 and d3 are in the range: 0≦d1≦0.3,0≦d2≦0.3, 0≦d3≦0.3, and 0≦d1+d2+d3≦0.3.

Besides the recurring units described above, the polymer may havefurther copolymerized therein additional recurring units, for example,recurring units (e) having a non-leaving hydrocarbon group as describedin JP-A 2008-281980. Examples of the non-leaving hydrocarbon group otherthan those described in JP-A 2008-281980 include indene, acenaphthylene,and norbornadiene derivatives. Copolymerization of recurring units (e)having a non-leaving hydrocarbon group facilitates dissolution of thepolymer in organic solvent-based developer.

It is also possible to incorporate recurring units (f) having an oxiraneor oxetane ring into the polymer. Where recurring units (f) having anoxirane or oxetane ring are copolymerized in the polymer, the exposedregion of resist film will be crosslinked, leading to improvements infilm retention of the exposed region and etch resistance. Examples ofthe recurring units (f) having an oxirane or oxetane ring are givenbelow wherein R⁴¹ is hydrogen or methyl.

The subscripts a1, a2, b1, b2, b3, b4, c, d1, d2, d3, e, and findicative of proportions of corresponding recurring units are in therange: 0≦a1<1.0, 0≦a2<1.0, 0≦b1<1.0, 0≦b2≦1.0, 0≦b3<1.0, 0≦b4<1.0,0<c<1.0, 0≦d1≦0.3, 0≦d2≦0.3, 0≦d3≦0.3, 0≦d1+d2+d3≦0.3, 0≦e≦0.4, and0≦f≦0.6;

preferably 0.1≦a1≦0.9, 0≦a2≦0.9, 0.1≦a1+a2≦0.9, 0≦b1≦0.9, 0≦b2≦0.9,0≦b3≦0.9, 0≦b4≦0.9, 0.1≦c≦0.9, 0≦d1≦0.2, 0≦d2≦0.2, 0≦d3≦0.2,0≦d1+d2+d3<0.2, 0≦e≦0.3, and 0≦f≦0.5, provided thata1+a2+b1+b2+b2+b4+c+d1+d2+d3+e+f=1.

The polymer serving as the base resin in the resist composition used inthe pattern forming process of the invention should preferably have aweight average molecular weight (Mw) in the range of 1,000 to 500,000,and more preferably 2,000 to 30,000, as measured by GPC versuspolystyrene standards using tetrahydrofuran solvent. With too low a Mw,a film thickness loss is likely to occur upon organic solventdevelopment. A polymer with too high a Mw may lose solubility in organicsolvent and have a likelihood of footing after pattern formation.

If a polymer has a wide molecular weight distribution or dispersity(Mw/Mn), which indicates the presence of lower and higher molecularweight polymer fractions, there is a possibility that followingexposure, foreign matter is left on the pattern or the pattern profileis exacerbated. The influences of molecular weight and dispersity becomestronger as the pattern rule becomes finer. Therefore, themulti-component copolymer should preferably have a narrow dispersity(Mw/Mn) of 1.0 to 2.0, especially 1.0 to 1.5, in order to provide aresist composition suitable for micropatterning to a small feature size.

The polymer used herein may be synthesized by any desired method, forexample, by dissolving unsaturated bond-containing monomerscorresponding to the respective units (a1), (a2), (b1), (b2), (b3),(b4), (c), (d1), (d2), (d3), (e), and (f) in an organic solvent, addinga radical initiator thereto, and effecting heat polymerization. Examplesof the organic solvent which can be used for polymerization includetoluene, benzene, tetrahydrofuran, diethyl ether and dioxane. Examplesof the polymerization initiator used herein include2,2′-azobisisobutyronitrile (AIBN),2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide.Preferably the system is heated at 50 to 80° C. for polymerization totake place. The reaction time is 2 to 100 hours, preferably 5 to 20hours. The acid labile group that has been incorporated in the monomermay be kept as such, or the product may be protected or partiallyprotected after polymerization.

It is acceptable to use a blend of two or more polymers which differ incompositional ratio, molecular weight or dispersity as well as a blendof an inventive polymer and another polymer free of acid labilegroup-substituted carboxyl having formula (1) or a blend of an inventivepolymer and a polymer comprising recurring units having an acid labilegroup-substituted hydroxyl group or an acid labile group-substitutedcarboxyl group, for example, a polymer comprising recurring unitsselected from units (a2) and units (b1) to (b4).

In a further embodiment, the inventive polymer may be blended with apolymer of the conventional type wherein the exposed region is dissolvedon alkaline development such as (meth)acrylate polymer, polynorbornene,cycloolefin-maleic anhydride copolymer, or ring-opening metathesispolymerization (ROMP) polymer. Also, the inventive polymer may beblended with a (meth)acrylate polymer having an acid labilegroup-substituted hydroxyl group wherein the exposed region is notdissolved by alkaline development, but a negative pattern is formed byorganic solvent development.

The pattern forming process of the invention comprises the steps ofcoating a resist composition onto a substrate, prebaking the resistcomposition to form a resist film, exposing a selected region of theresist film to high-energy radiation, baking (PEB), and developing theexposed resist film with an organic solvent developer so that theunexposed region of film is dissolved and the exposed region of film isleft, thereby forming a negative tone resist pattern such as a hole ortrench pattern.

The resist composition of the invention may comprise the polymer definedabove, an organic solvent, and optionally, a compound capable ofgenerating an acid in response to high-energy radiation (known as “acidgenerator”), dissolution regulator, basic compound, surfactant,acetylene alcohol, and other components.

The resist composition used herein may include an acid generator inorder for the composition to function as a chemically amplified resistcomposition. Typical of the acid generator used herein is a photoacidgenerator (PAG) capable of generating an acid in response to actiniclight or radiation. The PAG may preferably be compounded in an amount of0.5 to 30 parts and more preferably 1 to 20 parts by weight per 100parts by weight of the base resin. The PAG is any compound capable ofgenerating an acid upon exposure to high-energy radiation. Suitable PAGsinclude sulfonium salts, iodonium salts, sulfonyldiazomethane,N-sulfonyloxyimide, and oxime-O-sulfonate acid generators. The PAGs maybe used alone or in admixture of two or more. Typically acid generatorsgenerate such acids as sulfonic acids, imide acids and methide acids. Ofthese, sulfonic acids which are fluorinated at α-position are mostcommonly used. In case the acid labile group is an acetal group which issusceptible to deprotection, the sulfonic acid need not necessarily befluorinated at α-position. In the embodiment wherein the base polymerhas recurring units (d1), (d2) or (d3) of acid generator copolymerizedtherein, the acid generator need not be separately added.

Examples of the organic solvent used herein are described in JP-A2008-111103, paragraphs [0144] to [0145](U.S. Pat. No. 7,537,880).Specifically, exemplary solvents include ketones such as cyclohexanoneand methyl-2-n-amyl ketone; alcohols such as 3-methoxybutanol,3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, and1-ethoxy-2-propanol; ethers such as propylene glycol monomethyl ether,ethylene glycol monomethyl ether, propylene glycol monoethyl ether,ethylene glycol monoethyl ether, propylene glycol dimethyl ether, anddiethylene glycol dimethyl ether; esters such as propylene glycolmonomethyl ether acetate (PGMEA), propylene glycol monoethyl etheracetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butyl acetate,tert-butyl propionate, and propylene glycol mono-tert-butyl etheracetate; and lactones such as γ-butyrolactone, and mixtures thereof.Where an acid labile group of acetal form is used, a high-boilingalcohol solvent such as diethylene glycol, propylene glycol, glycerol,1,4-butane diol or 1,3-butane diol may be added for acceleratingdeprotection reaction of acetal.

Basic compounds, typically amines may be added to the resistcomposition. Suitable basic compounds include primary, secondary andtertiary amine compounds, specifically amine compounds having ahydroxyl, ether, ester, lactone, cyano or sulfonate group, as describedin JP-A 2008-111103, paragraphs [0146] to [0164], and compounds having acarbamate group, as described in JP 3790649.

Onium salts such as sulfonium salts, iodonium salts and ammonium saltsof sulfonic acids which are not fluorinated at α-position as describedin US 2008153030 (JP-A 2008-158339) and similar onium salts ofcarboxylic acid as described in JP 3991462 may be used as the quencher.Where the acid labile group is an acetal group which is very sensitiveto acid, the acid for eliminating the protective group need notnecessarily be an α-position fluorinated sulfonic acid, imidic acid, ormethidic acid because sometimes deprotection reaction may proceed evenwith an α-position non-fluorinated sulfonic acid. In this case, an oniumsalt of sulfonic acid cannot be used as the quencher, and instead, anonium salt of carboxylic acid is preferably used alone.

Exemplary surfactants are described in JP-A 2008-111103, paragraphs[0165] to [0166]. Exemplary dissolution regulators are described in JP-A2008-122932 (US 2008090172), paragraphs [0155] to [0178], and exemplaryacetylene alcohols in paragraphs [0179] to [0182].

Also a polymeric additive may be added for improving the waterrepellency on surface of a resist film as spin coated. This additive maybe used in the topcoatless immersion lithography. These additives have aspecific structure with a 1,1,1,3,3,3-hexafluoro-2-propanol residue andare described in JP-A 2007-297590 and JP-A 2008-111103. The waterrepellency improver to be added to the resist should be soluble in theorganic solvent as the developer. The water repellency improver ofspecific structure with a 1,1,1,3,3,3-hexafluoro-2-propanol residue iswell soluble in the developer. A polymer having an amino group or aminesalt copolymerized as recurring units may serve as the water repellentadditive and is effective for preventing evaporation of acid during PEBand avoiding any hole pattern opening failure after development. Anappropriate amount of the water repellency improver is 0.1 to 20 parts,preferably 0.5 to 10 parts by weight per 100 parts by weight of the baseresin.

Notably, an appropriate amount of the organic solvent is 100 to 10,000parts, preferably 300 to 8,000 parts by weight, and an appropriateamount of the basic compound is 0.0001 to 30 parts, preferably 0.001 to20 parts by weight, per 100 parts by weight of the base resin. Amountsof the dissolution regulator, surfactant, and acetylene alcohol may bedetermined as appropriate depending on their purpose of addition.

Process

FIG. 1 illustrates the pattern forming process of the invention. First,the positive resist composition is coated on a substrate to form aresist film thereon. Specifically, a resist film 40 of a positive resistcomposition is formed on a processable substrate 20 disposed on asubstrate 10 directly or via an intermediate intervening layer 30 asshown in FIG. 1A. The resist film preferably has a thickness of 10 to1,000 nm and more preferably 20 to 500 nm. Prior to exposure, the resistfilm is heated or prebaked, preferably at a temperature of 60 to 180°C., especially 70 to 150° C. for a time of 10 to 300 seconds, especially15 to 200 seconds.

The substrate 10 used herein is generally a silicon substrate. Theprocessable substrate (or target film) 20 used herein includes SiO₂,SiN, SiON, SiOC, p-Si, α-Si, TiN, WSi, BPSG, SOG, Cr, CrO, CrON, MoSi,low dielectric film, and etch stopper film. The intermediate interveninglayer 30 includes hard masks of SiO₂, SiN, SiON or p-Si, an undercoat inthe form of carbon film, a silicon-containing intermediate film, and anorganic antireflective coating.

Next comes exposure depicted at 50 in FIG. 1B. For the exposure,preference is given to high-energy radiation having a wavelength of 140to 250 nm, EUV having a wavelength of 13.5 nm, and EB, and especiallyArF excimer laser radiation of 193 nm. The exposure may be done eitherin a dry atmosphere such as air or nitrogen stream or by immersionlithography in water. The ArF immersion lithography uses deionized wateror liquids having a refractive index of at least 1 and highlytransparent to the exposure wavelength such as alkanes as the immersionsolvent. The immersion lithography involves prebaking a resist film andexposing the resist film to light through a projection lens, with waterintroduced between the resist film and the projection lens. Since thisallows lenses to be designed to a NA of 1.0 or higher, formation offiner feature size patterns is possible. The immersion lithography isimportant for the ArF lithography to survive to the 45-nm node. In thecase of immersion lithography, deionized water rinsing (or post-soaking)may be carried out after exposure for removing water droplets left onthe resist film, or a protective film may be applied onto the resistfilm after pre-baking for preventing any leach-out from the resist filmand improving water slip on the film surface.

The resist protective film used in the immersion lithography ispreferably formed from a solution of a polymer having1,1,1,3,3,3-hexafluoro-2-propanol residues which is insoluble in water,but soluble in an alkaline developer liquid, in a solvent selected fromalcohols of at least 4 carbon atoms, ethers of 8 to 12 carbon atoms, andmixtures thereof. The protective film-forming composition used hereinmay be based on a polymer comprising recurring units derived from amonomer having a 1,1,1,3,3,3-hexafluoro-2-propanol residue. While theprotective film must dissolve in the organic solvent developer, thepolymer comprising recurring units derived from a monomer having a1,1,1,3,3,3-hexafluoro-2-propanol residue dissolves in organic solventdevelopers. In particular, protective film-forming materials having1,1,1,3,3,3-hexafluoro-2-propanol residues as described in JP-A2007-025634 and JP-A 2008-003569 readily dissolve in organic solventdevelopers.

In the protective film-forming composition, an amine compound or aminesalt or a polymer having copolymerized therein recurring unitscontaining an amine compound or amine salt may be used. This componentis effective for controlling diffusion of the acid generated in theexposed region of the photoresist film to the unexposed region forthereby preventing any hole opening failure. Useful protective filmmaterials having an amine compound added thereto are described in JP-A2008-003569, and useful protective film materials having an amino groupor amine salt copolymerized are described in JP-A 2007-316448. The aminecompound or amine salt may be selected from the compounds enumerated asthe basic compound to be added to the resist composition. An appropriateamount of the amine compound or amine salt added is 0.01 to 10 parts,preferably 0.02 to 8 parts by weight per 100 parts by weight of the baseresin.

After formation of the photoresist film, deionized water rinsing (orpost-soaking) may be carried out for extracting the acid generator andthe like from the film surface or washing away particles, or afterexposure, rinsing (or post-soaking) may be carried out for removingwater droplets left on the resist film. If the acid evaporating from theexposed region during PEB deposits on the unexposed region to deprotectthe protective group on the surface of the unexposed region, there is apossibility that the surface edges of holes after development arebridged to close the holes. Particularly in the case of negativedevelopment, regions surrounding the holes receive light so that acid isgenerated therein. There is a possibility that the holes are not openedif the acid outside the holes evaporates and deposits inside the holesduring PEB. Provision of a protective film is effective for preventingevaporation of acid and for avoiding any hole opening failure. Aprotective film having an amine compound added thereto is more effectivefor preventing acid evaporation. On the other hand, a protective film towhich an acid compound such as a carboxyl or sulfo group is added orwhich is based on a polymer having copolymerized therein monomeric unitscontaining a carboxyl or sulfo group is undesirable because of apotential hole opening failure.

The other embodiment of the invention is a process for forming a patternby applying a resist composition comprising a polymer comprisingrecurring units having a carboxyl group substituted with an acid labilegroup of formula (1), an optional acid generator, and an organic solventonto a substrate, baking the composition to form a resist film, forminga protective film on the resist film, exposing the resist film tohigh-energy radiation to define exposed and unexposed regions, baking,and applying a developer to the coated substrate to form a negativepattern wherein the unexposed region of resist film and the protectivefilm are dissolved and the exposed region of resist film is notdissolved. The protective film is preferably formed from a compositioncomprising a polymer bearing a 1,1,1,3,3,3-hexafluoro-2-propanol residueand an amino group or amine salt-containing compound, or a compositioncomprising a polymer bearing a 1,1,1,3,3,3-hexafluoro-2-propanol residueand having amino group or amine salt-containing recurring unitscopolymerized, the composition further comprising an alcohol solvent ofat least 4 carbon atoms, an ether solvent of 8 to 12 carbon atoms, or amixture thereof.

Examples of suitable recurring units having a1,1,1,3,3,3-hexafluoro-2-propanol residue include those derived fromhydroxyl-bearing monomers selected from among the monomers listed forunits (c) on pages 51, 52 and 53. Examples of the amino group-containingcompound include the amine compounds described in JP-A 2008-111103,paragraphs [0146] to [0164] as being added to photoresist compositions.Examples of the amine salt-containing compound include salts of theforegoing amine compounds with carboxylic acids or sulfonic acids.

Suitable alcohols of at least 4 carbon atoms include 1-butyl alcohol,2-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol,2-pentanol, 3-pentanol, tert-amyl alcohol, neopentyl alcohol,2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl-3-pentanol,cyclopentanol, 1-hexanol, 2-hexanol, 3-hexanol, 2,3-dimethyl-2-butanol,3,3-dimethyl-1-butanol, 3,3-dimethyl-2-butanol, 2-ethyl-1-butanol,2-methyl-1-pentanol, 2-methyl-2-pentanol, 2-methyl-3-pentanol,3-methyl-1-pentanol, 3-methyl-2-pentanol, 3-methyl-3-pentanol,4-methyl-1-pentanol, 4-methyl-2-pentanol, 4-methyl-3-pentanol,cyclohexanol, and 1-octanol. Suitable ether solvents of 8 to 12 carbonatoms include di-n-butyl ether, diisobutyl ether, di-sec-butyl ether,di-n-pentyl ether, diisopentyl ether, di-sec-pentyl ether, di-t-amylether, and di-n-hexyl ether.

Exposure is preferably performed in an exposure dose of about 1 to 200mJ/cm², more preferably about 10 to 100 mJ/cm². This is followed bybaking (PEB) on a hot plate at 60 to 150° C. for 1 to 5 minutes,preferably at 80 to 120° C. for 1 to 3 minutes.

Thereafter the exposed resist film is developed in a developerconsisting of an organic solvent for 0.1 to 3 minutes, preferably 0.5 to2 minutes by any conventional techniques such as dip, puddle and spraytechniques. In this way, the unexposed region of resist film wasdissolved away, leaving a negative resist pattern 40 on the substrate 10as shown in FIG. 1C. The developer used herein is preferably selectedfrom among ketones such as 2-octanone, 2-nonanone, 2-heptanone,3-heptanone, 4-heptanone, 2-hexanone, 3-hexanone, diisobutyl ketone,methylcyclohexanone, acetophenone, and methylacetophenone, and esterssuch as propyl acetate, butyl acetate, isobutyl acetate, amyl acetate,butenyl acetate, isoamyl acetate, propyl formate, butyl formate,isobutyl formate, amyl formate, isoamyl formate, methyl valerate, methylpentenoate, methyl crotonate, ethyl crotonate, methyl propionate, ethylpropionate, ethyl 3-ethoxypropionate, methyl lactate, ethyl lactate,propyl lactate, butyl lactate, isobutyl lactate, amyl lactate, isoamyllactate, methyl 2-hydroxyisobutyrate, ethyl 2-hydroxyisobutyrate, methylbenzoate, ethyl benzoate, phenyl acetate, benzyl acetate, methylphenylacetate, benzyl formate, phenylethyl formate, methyl3-phenylpropionate, benzyl propionate, ethyl phenylacetate, and2-phenylethyl acetate, and mixtures thereof. One or more of thesesolvents may be used as the developer. When a mixture of plural solventsis used, they may be mixed in any desired ratio. A surfactant may beadded to the developer while it may be selected from the same list ofcompounds as exemplified for the surfactant to be added to the resistcomposition.

At the end of development, the resist film is rinsed. As the rinsingliquid, a solvent which is miscible with the developer and does notdissolve the resist film is preferred. Suitable solvents includealcohols of 3 to 10 carbon atoms, ether compounds of 8 to 12 carbonatoms, alkanes, alkenes, and alkynes of 6 to 12 carbon atoms, andaromatic solvents. Specifically, suitable alkanes of 6 to 12 carbonatoms include hexane, heptane, octane, nonane, decane, undecane,dodecane, methylcyclopentane, dimethylcyclopentane, cyclohexane,methylcyclohexane, dimethylcyclohexane, cycloheptane, cyclooctane, andcyclononane. Suitable alkenes of 6 to 12 carbon atoms include hexene,heptene, octene, cyclohexene, methylcyclohexene, dimethylcyclohexene,cycloheptene, and cyclooctene. Suitable alkynes of 6 to 12 carbon atomsinclude hexyne, heptyne, and octyne. Suitable alcohols of 3 to 10 carbonatoms include n-propyl alcohol, isopropyl alcohol, 1-butyl alcohol,2-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol,2-pentanol, 3-pentanol, tert-amyl alcohol, neopentyl alcohol,2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl-3-pentanol,cyclopentanol, 1-hexanol, 2-hexanol, 3-hexanol, 2,3-dimethyl-2-butanol,3,3-dimethyl-1-butanol, 3,3-dimethyl-2-butanol, 2-ethyl-1-butanol,2-methyl-1-pentanol, 2-methyl-2-pentanol, 2-methyl-3-pentanol,3-methyl-1-pentanol, 3-methyl-2-pentanol, 3-methyl-3-pentanol,4-methyl-1-pentanol, 4-methyl-2-pentanol, 4-methyl-3-pentanol,cyclohexanol, and 1-octanol. Suitable ether compounds of 8 to 12 carbonatoms include di-n-butyl ether, diisobutyl ether, di-sec-butyl ether,di-n-pentyl ether, diisopentyl ether, di-sec-pentyl ether, di-t-amylether, and di-n-hexyl ether. The solvents may be used alone or inadmixture. Besides the foregoing solvents, aromatic solvents may beused, for example, toluene, xylene, ethylbenzene, isopropylbenzene,tert-butylbenzene and mesitylene. Rinsing is effective for minimizingthe risks of resist pattern collapse and defect formation.

However, rinsing is not essential. If rinsing is omitted, the amount ofsolvent used may be reduced.

A hole pattern after reversal may be shrunk by the RELACS® process. Ahole pattern is shrunk by coating a shrink agent thereto, and bakingsuch that the shrink agent may undergo crosslinking at the resistsurface as a result of the acid catalyst diffusing from the resist layerduring bake, and the shrink agent may attach to the sidewall of the holepattern. The bake is at a temperature of 70 to 180° C., preferably 80 to170° C., for a time of 10 to 300 seconds. The extra shrink agent isstripped and the hole pattern is shrunk.

Where a hole pattern is formed by negative tone development, exposure bydouble dipole illuminations of X- and Y-direction line patterns providesthe highest contrast light. The contrast may be further increased bycombining dipole illumination with s-polarized illumination.

When a halftone phase shift mask bearing a lattice-like shifter patternis used, a pattern of holes may be formed at the intersections betweengratings of the lattice-like shifter pattern after development, asdescribed in JP-A 2011-170316, paragraph [0097](US 20110177462). Thepreferred halftone phase shift mask bearing a lattice-like shifterpattern has a transmittance of 3 to 15%. More preferably, the phaseshift mask used is a phase shift mask including a lattice-like firstshifter having a line width equal to or less than a half pitch and asecond shifter arrayed on the first shifter and consisting of lineswhose on-wafer size is 2 to 30 nm thicker than the line width of thefirst shifter, whereby a pattern of holes is formed only where the thickshifter is arrayed. Also preferably, the phase shift mask used is aphase shift mask including a lattice-like first shifter having a linewidth equal to or less than a half pitch and a second shifter arrayed onthe first shifter and consisting of dots whose on-wafer size is 2 to 100nm thicker than the line width of the first shifter, whereby a patternof holes is formed only where the thick shifter is arrayed.

Exposure by double dipole illuminations of X- and Y-direction linescombined with polarized illumination presents a method of forming lightof the highest contrast. This method, however, has the drawback that thethroughput is substantially reduced by double exposures and maskexchange therebetween. To continuously carry out two exposures whileexchanging a mask, the exposure tool must be equipped with two maskstages although the existing exposure tool includes a single mask stage.Higher throughputs may be obtained by carrying out exposure of Xdirection lines continuously on 25 wafers in a front-opening unified pod(FOUP), exchanging the mask, and carrying out exposure continuously onthe same 25 wafers, rather than exchanging a mask on every exposure of asingle wafer. However, a problem arises that as the time duration untilthe first one of 25 wafers is exposed in the second exposure isprolonged, the environment affects the resist such that the resist afterdevelopment may change its size and shape. To block the environmentalimpact on wafers in standby until the second exposure, it is effectivethat the resist film is overlaid with a protective film.

To proceed with a single mask, it is proposed in Non-Patent Document 1to carry out two exposures by dipole illuminations in X and Y directionsusing a mask bearing a lattice-like pattern. When this method iscompared with the above method using two masks, the optical contrast issomewhat reduced, but the throughput is improved by the use of a singlemask. As described in Non-Patent Document 1, the method involves formingX-direction lines in a first photoresist film by X-direction dipoleillumination using a mask bearing a lattice-like pattern, insolubilizingthe X-direction lines by light irradiation, coating a second photoresistfilm thereon, and forming Y-direction lines by Y-direction dipoleillumination, thereby forming holes at the interstices between X- andY-direction lines. Although only a single mask is needed, this methodincludes additional steps of insolubilizing the first photoresistpattern between the two exposures, and coating and developing the secondphotoresist film. Then the wafer must be removed from the exposure stagebetween the two exposures, giving rise to the problem of an increasedalignment error. To minimize the alignment error between two exposures,two exposures must be continuously carried out without removing thewafer from the exposure stage. The addition of s-polarized illuminationto dipole illumination provides a further improved contrast and is thuspreferably employed. After two exposures for forming X- and Y-directionlines using a lattice-like mask are performed in an overlapping manner,negative tone development is performed whereupon a hole pattern isformed.

When it is desired to form a hole pattern via a single exposure using alattice-like mask, a quadra-pole illumination or cross-pole illuminationis used. The contrast may be improved by combining it with X-Y polarizedillumination or azimuthally polarized illumination of circularpolarization.

In the hole pattern forming process using the resist composition of theinvention, when two exposures are involved, these exposures are carriedout by changing the illumination and mask for the second exposure fromthose for the first exposure, whereby a fine size pattern can be formedat the highest contrast and to dimensional uniformity. The masks used inthe first and second exposures bear first and second patterns ofintersecting lines whereby a pattern of holes at intersections of linesis formed in the resist film after development. The first and secondlines are preferably at right angles although an angle of intersectionother than 90° may be employed. The first and second lines may have thesame or different size and/or pitch. If a single mask bearing firstlines in one area and second lines in a different area is used, it ispossible to perform first and second exposures continuously. In thiscase, however, the maximum area available for exposure is one half.Notably, the continuous exposures lead to a minimized alignment error.Of course, the single exposure provides a smaller alignment error thanthe two continuous exposures.

When two exposures are performed using a single mask without reducingthe exposure area, the mask pattern may be a lattice-like pattern, a dotpattern, or a combination of a dot pattern and a lattice-like pattern.The use of a lattice-like pattern contributes to the most improved lightcontrast, but has the drawback of a reduced resist sensitivity due to alowering of light intensity. On the other hand, the use of a dot patternsuffers a lowering of light contrast, but provides the merit of animproved resist sensitivity.

Where holes are arrayed in horizontal and vertical directions, theabove-described illumination and mask pattern are used. Where holes arearrayed at a different angle, for example, at an angle of 45°, a mask ofa 45° arrayed pattern is combined with dipole illumination or cross-poleillumination.

Where two exposures are performed, a first exposure by a combination ofdipole illumination with polarized illumination for enhancing thecontrast of X-direction lines is followed by a second exposure by acombination of dipole illumination with polarized illumination forenhancing the contrast of Y-direction lines. Two continuous exposureswith the X- and Y-direction contrasts emphasized through a single maskcan be performed on a currently commercially available scanner.

The method of combining X and Y polarized illuminations with cross-poleillumination using a mask bearing a lattice-like pattern can form a holepattern through a single exposure, despite a slight lowering of lightcontrast as compared with two exposures of dipole illumination. Themethod is estimated to attain a substantial improvement in throughputand avoids the problem of misalignment between two exposures. Using sucha mask and illumination, a hole pattern of the order of 40 nm can beformed at a practically acceptable cost.

On use of a mask bearing a lattice-like pattern, light is fully shieldedat intersections between gratings. A fine hole pattern may be formed byperforming exposure through a mask bearing such a pattern and organicsolvent development entailing positive/negative reversal.

On use of a mask bearing a dot pattern, although the contrast of anoptical image is low as compared with the lattice-like pattern mask, theformation of a hole pattern is possible owing to the presence of blackor light shielded spots.

It is difficult to form a fine hole pattern that holes are randomlyarrayed at varying pitch and position. The super-resolution technologyusing off-axis illumination (such as dipole or cross-pole illumination)in combination with a phase shift mask and polarization is successful inimproving the contrast of dense (or grouped) patterns, but not so thecontrast of isolated patterns.

When the super-resolution technology is applied to repeating densepatterns, the pattern density bias between dense and isolated patterns,known as proximity bias, becomes a problem. As the super-resolutiontechnology used becomes stronger, the resolution of a dense pattern ismore improved, but the resolution of an isolated pattern remainsunchanged. Then the proximity bias is exaggerated. In particular, anincrease of proximity bias in a hole pattern resulting from furtherminiaturization poses a serious problem. One common approach taken tosuppress the proximity bias is by biasing the size of a mask pattern.Since the proximity bias varies with properties of a photoresistcomposition, specifically dissolution contrast and acid diffusion, theproximity bias of a mask varies with the type of photoresistcomposition. For a particular type of photoresist composition, a maskhaving a different proximity bias must be used. This adds to the burdenof mask manufacturing. Then the pack and unpack (PAU) method is proposedin Proc. SPIE Vol. 5753, p 171 (2005), which involves strongsuper-resolution illumination of a first positive resist to resolve adense hole pattern, coating the first positive resist pattern with anegative resist film material in alcohol solvent which does not dissolvethe first positive resist pattern, exposure and development of anunnecessary hole portion to close the corresponding holes, therebyforming both a dense pattern and an isolated pattern. One problem of thePAU method is misalignment between first and second exposures, as theauthors point out in the report. The hole pattern which is not closed bythe second development experiences two developments and thus undergoes asize change, which is another problem.

To form a random pitch hole pattern by organic solvent developmententailing positive/negative reversal, a mask is used in which alattice-like pattern is arrayed over the entire surface and the width ofgratings is thickened only where holes are to be formed as described inJP-A 2011-170316, paragraph [0102].

Also useful is a mask in which a lattice-like pattern is arrayed overthe entire surface and thick dots are disposed only where holes are tobe formed.

On use of a mask bearing no lattice-like pattern arrayed, holes aredifficult to form, or even if holes are formed, a variation of mask sizeis largely reflected by a variation of hole size because the opticalimage has a low contrast.

EXAMPLE

Examples of the invention are given below by way of illustration and notby way of limitation. The abbreviation “pbw” is parts by weight. For allpolymers, Mw and Mn are determined by GPC versus polystyrene standardsusing tetrahydrofuran solvent. For measurement of the hole size of apattern, a top-down scanning electron microscope (TDSEM) CG-4000(Hitachi High-Technologies Corp.) was used.

Synthesis Example

Various polymers (Resist Polymers 1 to 10, Comparative Resist Polymers 1to 7, Blend Resist Polymers 1 and 2) for use in resist compositions wereprepared by combining suitable monomers, effecting copolymerizationreaction in tetrahydrofuran solvent, pouring into methanol forcrystallization, repeatedly washing with hexane, isolation, and drying.The polymers were analyzed by ¹H-NMR to determine their composition andby GPC to determine Mw and dispersity Mw/Mn.

Preparation of Resist Composition

A resist composition in solution form was prepared by dissolving apolymer (Resist Polymer) and components in solvents in accordance withthe formulation of Table 1 and filtering through a Teflon® filter with apore size of 0.2 m. The components used herein are identified below.

-   Acid generator: PAG1 to PAG6 of the following structural formulae

Quenchers 1 to 7 of the following structural formulae

Organic Solvent:

PGMEA (propylene glycol monomethyl ether acetate)

CyH (cyclohexanone)

TABLE 1 Acid Basic Organic Polymer generator compound Additive solvent(pbw) (pbw) (pbw) (pbw) (pbw) Resist 1 Resist Polymer 1 PAG1 Quencher 1Water-repellent PGMEA(2,000) (100) (5.0) (2.00) Polymer 1 CyH(500) (3) 2Resist Polymer 2 PAG1 Quencher 2 Water-repellent PGMEA(2,000) (100)(5.0) (2.00) Polymer 1 CyH(500) (3) 3 Resist Polymer 3 PAG1 Quencher 3Water-repellent PGMEA(2,000) (100) (4.0) (4.00) Polymer 1 CyH(500) (3) 4Resist Polymer 4 PAG2 Quencher 1 Water-repellent PGMEA(2,000) (100)(5.0) (2.00) Polymer 1 CyH(500) (3) 5 Resist Polymer 5 PAG3 Quencher 1Water-repellent PGMEA(2,000) (100) (5.0) (2.00) Polymer 1 CyH(500) (3) 6Resist Polymer 6 PAG4 Quencher 3 Water-repellent PGMEA(2,000) (100)(4.0) (4.00) Polymer 1 CyH(500) (3) 7 Resist Polymer 7 PAG4 Quencher 4Water-repellent PGMEA(2,000) (100) (4.0) (4.00) Polymer 1 CyH(500) (3) 8Resist Polymer 8 PAG5 Quencher 5 Water-repellent PGMEA(2,000) (100)(5.5) (4.00) Polymer 1 CyH(500) (3) 9 Resist Polymer 9 — Quencher 2Water-repellent PGMEA(2,000) (100) (2.00) Polymer 1 CyH(500) (3) 10Resist Polymer 1 PAG1 Quencher 1 Water-repellent PGMEA(2,000) (60) (5.0)(2.00) Polymer 1 CyH(500) Comparative Resist Polymer 1 (3) (40) 11Resist Polymer 1 PAG6 Quencher 6 Water-repellent PGMEA(2,000) (60) (4.0)(4.00) Polymer 1 CyH(500) Blend Resist Polymer 1 (3) (40) 12 ResistPolymer 1 PAG6 Quencher 7 Water-repellent PGMEA(2,000) (60) (4.0) (4.00)Polymer 1 CyH(500) Blend Resist Polymer 2 (3) (40) 13 Resist Polymer 10PAG1 Quencher 1 — PGMEA(2,000) (100) (15.0) (1.50) CyH(500) ComparativeResist 1 Comparative Resist Polymer 1 PAG1 Quencher 1 Water-repellentPGMEA(2,000) (100) (5.0) (2.00) Polymer 1 CyH(500) (3) 2 ComparativeResist Polymer 2 PAG1 Quencher 1 Water-repellent PGMEA(2,000) (100)(5.0) (2.00) Polymer 1 CyH(500) (3) 3 Comparative Resist Polymer 3 PAG1Quencher 1 Water-repellent PGMEA(2,000) (100) (5.0) (2.00) Polymer 1CyH(500) (3) 4 Comparative Resist Polymer 4 PAG1 Quencher 1Water-repellent PGMEA(2,000) (100) (5.0) (2.00) Polymer 1 CyH(500) (3) 5Comparative Resist Polymer 5 PAG1 Quencher 1 Water-repellentPGMEA(2,000) (100) (5.0) (2.00) Polymer 1 CyH(500) (3) 6 ComparativeResist Polymer 6 PAG1 Quencher 1 Water-repellent PGMEA(2,000) (100)(5.0) (2.00) Polymer 1 CyH(500) (3) 7 Comparative Resist Polymer 7 PAG1Quencher 1 — PGMEA(2,000) (100) (15.0)  (1.50) CyH(500)

Examples and Comparative Examples ArF Lithography Patterning Test 1

On a substrate (silicon wafer), a spin-on carbon film ODL-50 (Shin-EtsuChemical Co., Ltd.) having a carbon content of 80 wt % was deposited toa thickness of 200 nm and a silicon-containing spin-on hard maskSHB-A940 having a silicon content of 43 wt % was deposited thereon to athickness of 35 nm. On this substrate for trilayer process, the resistcomposition in Table 2 was spin coated, then baked on a hot plate at100° C. for 60 seconds to form a resist film of 100 nm thick.

Using an ArF excimer laser immersion lithography scanner NSR-610C (NikonCorp., NA 1.30, a 0.98/0.78, cross-pole opening 20 deg., azimuthallypolarized illumination), exposure was performed in a varying dosethrough a 6% halftone phase shift mask bearing a lattice-like patternwith a pitch of 90 nm and a line width of 30 nm (on-wafer size). Afterthe exposure, the wafer was baked (PEB) at the temperature shown inTable 2 for 60 seconds and developed. Specifically, butyl acetate wasinjected from a development nozzle while the wafer was spun at 30 rpmfor 3 seconds, which was followed by stationary puddle development for27 seconds. The wafer was rinsed with diisoamyl ether, spin dried, andbaked at 100° C. for 20 seconds to evaporate off the rinse liquid,yielding a negative pattern.

A hole pattern resulted from image reversal by solvent development. Byobservation under TDSEM CG-4000, the size of 50 holes was measured, fromwhich a size variation 30 was determined. The cross-sectional profile ofthe hole pattern was observed under electron microscope S-4300 (HitachiHigh Technologies Corp.). The results are shown in Table 2. It isevident that the resist compositions within the scope of the inventionform patterns having dimensional uniformity and a perpendicular profileafter organic solvent development.

TABLE 2 Hole size PEB temp. Dose Pattern variation Resist (° C.)(mJ/cm²) Developer profile 3σ (nm) Example 1-1 Resist 1 95 34 n-butylacetate perpendicular 2.1 1-2 Resist 2 90 35 n-butyl acetateperpendicular 2.3 1-3 Resist 3 95 26 n-butyl acetate perpendicular 2.21-4 Resist 4 90 27 n-butyl acetate perpendicular 2.2 1-5 Resist 5 95 26n-butyl acetate perpendicular 2.4 1-6 Resist 6 90 27 n-butyl acetateperpendicular 2.4 1-7 Resist 7 95 28 n-butyl acetate perpendicular 2.41-8 Resist 8 95 25 n-butyl acetate perpendicular 2.3 1-9 Resist 9 95 23n-butyl acetate perpendicular 2.5 1-10 Resist 7 90 28 n-butyl acetateperpendicular 2.4 1-11 Resist 8 90 25 n-butyl acetate perpendicular 2.31-12 Resist 9 90 23 n-butyl acetate perpendicular 2.5 1-13 Resist 10 9528 n-butyl acetate perpendicular 2.4 1-14 Resist 11 95 25 n-butylacetate perpendicular 2.3 1-15 Resist 12 95 23 n-butyl acetateperpendicular 2.5 1-16 Resist 3 95 32 2-heptanone perpendicular 2.4 1-17Resist 3 95 38 methyl benzoate perpendicular 2.3 1-18 Resist 3 95 39ethyl benzoate perpendicular 2.5 Comparative 1-1 Comparative 95 42n-butyl acetate inversely tapered 4.0 Example Resist 1 1-2 Comparative95 40 n-butyl acetate inversely tapered 3.8 Resist 2 1-3 Comparative 9539 n-butyl acetate inversely tapered 3.7 Resist 3 1-4 Comparative 95 37n-butyl acetate inversely tapered 3.5 Resist 4 1-5 Comparative 95 35n-butyl acetate inversely tapered 3.2 Resist 5 1-6 Comparative 110 30n-butyl acetate inversely tapered 5.5 Resist 6

ArF Lithography Patterning Test 2

On a substrate (silicon wafer), a spin-on carbon film ODL-50 (Shin-EtsuChemical Co., Ltd.) having a carbon content of 80 wt % was deposited toa thickness of 200 nm and a silicon-containing spin-on hard maskSHB-A940 having a silicon content of 43 wt % was deposited thereon to athickness of 35 nm. On this substrate for trilayer process, the resistcomposition in Table 3 was spin coated, then baked on a hot plate at100° C. for 60 seconds to form a resist film of 80 nm thick.

Using an ArF excimer laser immersion lithography scanner NSR-610C (NikonCorp., NA 1.30, σ0.98/0.78, cross-pole opening 20 deg., azimuthallypolarized illumination), exposure was performed through a 6% halftonephase shift mask bearing a line-and-space pattern with a pitch of 90 nmand a width of 50 nm (on-wafer size) while the dose was varied. Afterthe exposure, the wafer was baked (PEB) at the temperature shown inTable 3 for 60 seconds and developed. Specifically, the developer shownin Table 3 was injected from a development nozzle while the wafer wasspun at 30 rpm for 3 seconds, which was followed by stationary puddledevelopment for 27 seconds. The wafer was rinsed with4-methyl-2-pentanol, spin dried, and baked at 100° C. for 20 seconds toevaporate off the rinse liquid, yielding a negative pattern.

A hole pattern resulted from image reversal by solvent development. Thesize of holes was measured under TDSEM CG-4000. The LWR of those spaceshaving a size of 50 nm±5 nm was determined. The minimum size of spaceswhich remained open without bridging when the exposure dose wasincreased was determined. The results are shown in Table 3.

TABLE 3 PEB temp. LWR Minimum space Resist (° C.) Developer (nm) size(nm) Example 2-1 Resist 1 95 n-butyl acetate 4.5 39 2-2 Resist 2 90n-butyl acetate 4.3 37 2-3 Resist 3 95 n-butyl acetate 4.4 38 2-4 Resist4 90 n-butyl acetate 4.2 36 2-5 Resist 5 95 n-butyl acetate 4.2 37 2-6Resist 6 90 n-butyl acetate 4.1 38 2-7 Resist 7 95 n-butyl acetate 4.036 2-8 Resist 8 95 n-butyl acetate 4.6 34 2-9 Resist 9 95 n-butylacetate 4.6 34 2-10 Resist 7 90 n-butyl acetate 4.5 36 2-11 Resist 8 90n-butyl acetate 4.6 36 2-12 Resist 9 90 n-butyl acetate 4.8 38 2-13Resist 10 95 n-butyl acetate 4.5 36 2-14 Resist 11 95 n-butyl acetate4.6 36 2-15 Resist 12 95 n-butyl acetate 4.8 38 2-16 Resist 1 952-heptanone 5.2 39 2-17 Resist 1 95 methyl benzoate 4.6 34 2-18 Resist 195 ethyl benzoate 4.6 31 Comparative 2-1 Comparative 95 n-butyl acetate6.3 44 Example Resist 1 2-2 Comparative 95 n-butyl acetate 6.2 42 Resist2 2-3 Comparative 95 n-butyl acetate 5.8 41 Resist 3 2-4 Comparative 95n-butyl acetate 5.6 43 Resist 4 2-5 Comparative 95 n-butyl acetate 5.541 Resist 5 2-6 Comparative 110 n-butyl acetate 6.9 48 Resist 6

EB Lithography Patterning Test

Using a coater/developer system Clean Track Mark 5 (Tokyo ElectronLtd.), the resist composition of Table 4 was spin coated onto a siliconsubstrate (diameter 6 inches, vapor primed with hexamethyldisilazane(HMDS)) and pre-baked on a hot plate at 110° C. for 60 seconds to form aresist film of 100 nm thick. Using a system HL-800D (Hitachi Ltd.) at aHV voltage of 50 kV, the resist film was exposed imagewise to EB in avacuum chamber.

Using Clean Track Mark 5, immediately after the imagewise exposure, theresist film was baked (PEB) on a hot plate at the temperature shown inTable 4 for 60 seconds and puddle developed in the developer shown inTable 4 for 30 seconds. The substrate was rinsed with diisoamyl ether,spin dried, and baked at 100° C. for 20 seconds to evaporate off therinse liquid, yielding a negative pattern.

Sensitivity is the exposure dose (μC/cm²) that provides a 1:1 resolutionof a 100-nm line-and-space pattern. Resolution is a minimum size at theexposure dose. The 100-nm L/S pattern was measured for LWR under SEM.The results are shown in Table 4.

TABLE 4 PEB temp. Sensitivity LWR Resist (° C.) Developer (μC/cm²) (nm)Example 3-1 Resist 13 95 n-butyl acetate 55 4.8 3-2 Resist 13 95 methylbenzoate 58 4.8 3-3 Resist 13 95 ethyl benzoate 59 4.9 Comparative 3-1Comparative 95 n-butyl acetate 52 8.6 Example Resist 8

While the invention has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention.Therefore, it is intended that the invention not be limited to theparticular embodiment disclosed as the best mode contemplated forcarrying out this invention, but that the invention will include allembodiments falling within the scope of the appended claims.

Japanese Patent Application No. 2012-137942 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A pattern forming process comprising the steps of: applying a resistcomposition comprising a polymer and an optional acid generator onto asubstrate, prebaking the composition to form a resist film, exposing theresist film to high-energy radiation, baking, and developing the exposedfilm in an organic solvent-based developer to form a negative patternwherein the unexposed region of film is dissolved away and the exposedregion of film is not dissolved, said polymer comprising recurring unitshaving a carboxyl group whose hydrogen is substituted by an acid labilegroup having the general formula (1):

wherein R¹ is a straight, branched or cyclic C₁-C₇ alkyl group, R², R³and R⁴ each are hydrogen, methyl or ethyl, excluding the event that atleast two of R², R³ and R⁴ are hydrogen, R⁵ is hydrogen or methyl, andR⁶ is methylene or ethylene.
 2. The process of claim 1 wherein therecurring units having a carboxyl group substituted with an acid labilegroup are units (a1) having the general formula (2):

wherein R⁷ is hydrogen or methyl, R⁸ is an acid labile group havingformula (1), X¹ is a single bond, phenylene, naphthylene, or—C(═O)—O—R⁹—, R⁹ is a straight, branched or cyclic C₁-C₁₀ alkylene groupwhich may contain an ether radical, ester radical, lactone ring orhydroxyl radical, or phenylene or naphthylene group, and 0<a1<1.0. 3.The process of claim 1 wherein the polymer further comprises recurringunits of at least one type selected from recurring units (a2) having thegeneral formula (3) and recurring units (b1) to (b4) having the generalformula (4):

wherein R¹⁰ is hydrogen or methyl, R¹¹ is an acid labile group differentfrom formula (1), X² is a single bond, phenylene, naphthylene or—C(═O)—O—R¹²—, R¹² is a straight, branched or cyclic C₁-C₁₀ alkylenegroup which may contain an ether radical, ester radical, lactone ring orhydroxyl radical, or phenylene or naphthylene group, and 0≦a2<1.0,

wherein R¹³ and R¹⁶ each are hydrogen or methyl, R¹⁴ is a straight,branched or cyclic, di- to penta-valent C₁-C₁₆ aliphatic hydrocarbongroup which may contain an ether or ester radical, R¹⁵ and R¹⁷ each arean acid labile group, R¹⁸ to R²¹ and R²² to R²⁵ are each independentlyhydrogen, cyano, a straight, branched or cyclic C₁-C₆ alkyl group,alkoxycarbonyl group, or ether or lactone ring-containing group, atleast one of R¹⁸ to R²¹ and R²² to R²⁵ has an acid labilegroup-substituted hydroxyl group, m is an integer of 1 to 4, n is 0 or1, b1, b2, b3 and b4 are in the range: 0≦b1<1.0, 0≦b2<1.0, 0≦b3<1.0,0≦b4<1.0, 0≦b1+b2+b3+b4<1.0, and 0<a2+b1+b2+b3+b4<1.0.
 4. The process ofclaim 1 wherein the polymer further comprises recurring units derivedfrom a monomer having an adhesive group selected from the classconsisting of hydroxyl, cyano, carbonyl, ester, ether, lactone ring,carboxyl, carboxylic anhydride, sulfonic acid ester, disulfone, andcarbonate.
 5. The process of claim 1 wherein the polymer furthercomprises recurring units (d1), (d2) or (d3) having the followinggeneral formula:

wherein R⁰²⁰, R⁰²⁴, and R⁰²⁸ each are hydrogen or methyl, R⁰²¹ is asingle bond, phenylene, —O—R⁰³³—, or —C(═O)—Y—R⁰³³—, Y is oxygen or NH,R⁰³³ is a straight, branched or cyclic C₁-C₆ alkylene group, alkenyleneor phenylene group, which may contain a carbonyl (—CO—), ester (—COO—),ether (—O—) or hydroxyl radical, R⁰²², R⁰²³, R⁰²⁵, R⁰²⁶, R⁰²⁷, R⁰²⁹,R⁰³⁰, and R⁰³¹ are each independently a straight, branched or cyclicC₁-C₁₂ alkyl group which may contain a carbonyl, ester or ether radical,or a C₆-C₁₂ aryl, C₇-C₂₀ aralkyl, or thiophenyl group, Z¹ is a singlebond, methylene, ethylene, phenylene, fluorophenylene, —O—R⁰³²—, or—C(═O)—Z²—R⁰³²—, Z² is oxygen or NH, R⁰³² is a straight, branched orcyclic C₁-C₆ alkylene group, alkenylene or phenylene group, which maycontain a carbonyl, ester, ether or hydroxyl radical, M⁻ is anon-nucleophilic counter ion, d1, d2 and d3 are in the range: 0≦d1≦0.3,0≦d2≦0.3, 0≦d3≦0.3, 0≦d1+d2+d3≦0.3.
 6. The process of claim 1 whereinthe developer comprises at least one organic solvent selected from thegroup consisting of 2-octanone, 2-nonanone, 2-heptanone, 3-heptanone,4-heptanone, 2-hexanone, 3-hexanone, diisobutyl ketone,methylcyclohexanone, acetophenone, methylacetophenone, propyl acetate,butyl acetate, isobutyl acetate, amyl acetate, isoamyl acetate, butenylacetate, propyl formate, butyl formate, isobutyl formate, amyl formate,isoamyl formate, methyl valerate, methyl pentenoate, methyl crotonate,ethyl crotonate, methyl propionate, ethyl propionate, ethyl3-ethoxypropionate, methyl lactate, ethyl lactate, propyl lactate, butyllactate, isobutyl lactate, amyl lactate, isoamyl lactate, methyl2-hydroxyisobutyrate, ethyl 2-hydroxyisobutyrate, methyl benzoate, ethylbenzoate, phenyl acetate, benzyl acetate, methyl phenylacetate, benzylformate, phenylethyl formate, methyl 3-phenylpropionate, benzylpropionate, ethyl phenylacetate, and 2-phenylethyl acetate.
 7. Theprocess of claim 1 wherein the step of exposing the resist film tohigh-energy radiation includes KrF excimer laser lithography ofwavelength 248 nm, ArF excimer laser lithography of wavelength 193 nm,EUV lithography of wavelength 13.5 nm or EB lithography.
 8. A patternforming process according to claim 1, comprising the steps of: applyinga resist composition onto a substrate, the resist composition comprisinga polymer comprising recurring units having a carboxyl group which issubstituted with an acid labile group having formula (1), an optionalacid generator, and an organic solvent, prebaking the composition toform a resist film, forming a protective film on the resist film,exposing the resist film to high-energy radiation, baking, and applyingan organic solvent-based developer to dissolve away the protective filmand the unexposed region of resist film for forming a negative patternwherein the exposed region of resist film is not dissolved.
 9. Anegative pattern-forming resist composition comprising a polymer, anacid generator, and an organic solvent, said polymer comprisingrecurring units (a1) having a carboxyl group which is substituted withan acid labile group having the general formula (1), the units (a1)having the general formula (2):

wherein R¹ is a straight, branched or cyclic C₁-C₇ alkyl group, R², R³and R⁴ each are hydrogen, methyl or ethyl, excluding the event that atleast two of R², R³ and R⁴ are hydrogen, R⁵ is hydrogen or methyl, andR⁶ is methylene or ethylene.

wherein R⁷ is hydrogen or methyl, R⁸ is an acid labile group havingformula (1), X¹ is a single bond, phenylene, naphthylene, or—C(═O)—O—R⁹—, R⁹ is a straight, branched or cyclic C₁-C₁₀ alkylene groupwhich may contain an ether radical, ester radical, lactone ring orhydroxyl radical, or phenylene or naphthylene group, and 0<a1<1.0, saidpolymer being dissolvable in a developer selected from the groupconsisting of 2-octanone, 2-nonanone, 2-heptanone, 3-heptanone,4-heptanone, 2-hexanone, 3-hexanone, diisobutyl ketone,methylcyclohexanone, acetophenone, methylacetophenone, propyl acetate,butyl acetate, isobutyl acetate, amyl acetate, isoamyl acetate, butenylacetate, propyl formate, butyl formate, isobutyl formate, amyl formate,isoamyl formate, methyl valerate, methyl pentenoate, methyl crotonate,ethyl crotonate, methyl propionate, ethyl propionate, ethyl3-ethoxypropionate, methyl lactate, ethyl lactate, propyl lactate, butyllactate, isobutyl lactate, amyl lactate, isoamyl lactate, methyl2-hydroxyisobutyrate, ethyl 2-hydroxyisobutyrate, methyl benzoate, ethylbenzoate, phenyl acetate, benzyl acetate, methyl phenylacetate, benzylformate, phenylethyl formate, methyl 3-phenylpropionate, benzylpropionate, ethyl phenylacetate, and 2-phenylethyl acetate.
 10. Theresist composition of claim 9 wherein the polymer further comprisesrecurring units of at least one type selected from recurring units (a2)having the general formula (3) and recurring units (b1) to (b4) havingthe general formula (4):

wherein R¹⁰ is hydrogen or methyl, R¹¹ is an acid labile group differentfrom formula (1), X² is a single bond, phenylene, naphthylene, or—C(═O)—O—R¹²—, R¹² is a straight, branched or cyclic C₁-C₁₀ alkylenegroup which may contain an ether radical, ester radical, lactone ring orhydroxyl radical, or phenylene or naphthylene group, and 0≦a2<1.0,

wherein R¹³ and R¹⁶ each are hydrogen or methyl, R¹⁴ is a straight,branched or cyclic, di- to penta-valent C₁-C₁₆ aliphatic hydrocarbongroup which may contain an ether or ester radical, R¹⁵ and R¹⁷ each arean acid labile group, R¹⁸ to R²¹ and R²² to R²⁵ are each independentlyhydrogen, cyano, a straight, branched or cyclic C₁-C₆ alkyl group,alkoxycarbonyl group, or ether or lactone ring-containing group, atleast one of R¹⁸ to R²¹ and R²² to R²⁵ has an acid labilegroup-substituted hydroxyl group, m is an integer of 1 to 4, n is 0 or1, b1, b2, b3 and b4 are in the range: 0≦b1<1.0, 0≦b2<1.0, 0≦b3<1.0,0≦b4<1.0, 0≦b1+b2+b3+b4<1.0, and 0<a2+b1+b2+b3+b4<1.0.
 11. The resistcomposition of claim 9 wherein the polymer further comprises recurringunits derived from a monomer having an adhesive group selected from theclass consisting of hydroxyl, cyano, carbonyl, ester, ether, lactonering, carboxyl, carboxylic anhydride, sulfonic acid ester, disulfone,and carbonate.
 12. The resist composition of claim 9 wherein the polymerfurther comprises recurring units (d1), (d2) or (d3) having thefollowing general formula:

wherein R⁰²⁰, R⁰²⁴, and R⁰²⁸ each are hydrogen or methyl, R⁰²¹ is asingle bond, phenylene, —O—R⁰³³—, or —C(═O)—Y—R⁰³³—, Y is oxygen or NH,R⁰³³ is a straight, branched or cyclic C₁-C₆ alkylene group, alkenyleneor phenylene group, which may contain a carbonyl (—CO—), ester (—COO—),ether (—O—) or hydroxyl radical, R⁰²², R⁰²³, R⁰²⁵, R⁰²⁶, R⁰²⁷, R⁰²⁹,R⁰³⁰, and R⁰³¹ are each independently a straight, branched or cyclicC₁-C₁₂ alkyl group which may contain a carbonyl, ester or ether radical,or a C₆-C₁₂ aryl, C₇-C₂₀ aralkyl, or thiophenyl group, Z¹ is a singlebond, methylene, ethylene, phenylene, fluorophenylene, —O—R⁰³²—, or—C(═O)—Z²—R⁰³²—, Z² is oxygen or NH, R⁰³² is a straight, branched orcyclic C₁-C₆ alkylene group, alkenylene or phenylene group, which maycontain a carbonyl, ester, ether or hydroxyl radical, M⁻ is anon-nucleophilic counter ion, d1, d2 and d3 are in the range: 0≦d1≦0.3,0≦d2≦0.3, 0≦d3≦0.3, 0<d1+d2+d3≦0.3.
 13. A pattern forming processaccording to claim 2, comprising the steps of: applying a resistcomposition onto a substrate, the resist composition comprising apolymer comprising recurring units having a carboxyl group which issubstituted with an acid labile group having formula (1), an optionalacid generator, and an organic solvent, prebaking the composition toform a resist film, forming a protective film on the resist film,exposing the resist film to high-energy radiation, baking, and applyingan organic solvent-based developer to dissolve away the protective filmand the unexposed region of resist film for forming a negative patternwherein the exposed region of resist film is not dissolved.
 14. Apattern forming process according to claim 3, comprising the steps of:applying a resist composition onto a substrate, the resist compositioncomprising a polymer comprising recurring units having a carboxyl groupwhich is substituted with an acid labile group having formula (1), anoptional acid generator, and an organic solvent, prebaking thecomposition to form a resist film, forming a protective film on theresist film, exposing the resist film to high-energy radiation, baking,and applying an organic solvent-based developer to dissolve away theprotective film and the unexposed region of resist film for forming anegative pattern wherein the exposed region of resist film is notdissolved.
 15. A pattern forming process according to claim 4,comprising the steps of: applying a resist composition onto a substrate,the resist composition comprising a polymer comprising recurring unitshaving a carboxyl group which is substituted with an acid labile grouphaving formula (1), an optional acid generator, and an organic solvent,prebaking the composition to form a resist film, forming a protectivefilm on the resist film, exposing the resist film to high-energyradiation, baking, and applying an organic solvent-based developer todissolve away the protective film and the unexposed region of resistfilm for forming a negative pattern wherein the exposed region of resistfilm is not dissolved.
 16. A pattern forming process according to claim5, comprising the steps of: applying a resist composition onto asubstrate, the resist composition comprising a polymer comprisingrecurring units having a carboxyl group which is substituted with anacid labile group having formula (1), an optional acid generator, and anorganic solvent, prebaking the composition to form a resist film,forming a protective film on the resist film, exposing the resist filmto high-energy radiation, baking, and applying an organic solvent-baseddeveloper to dissolve away the protective film and the unexposed regionof resist film for forming a negative pattern wherein the exposed regionof resist film is not dissolved.
 17. A pattern forming process accordingto claim 6, comprising the steps of: applying a resist composition ontoa substrate, the resist composition comprising a polymer comprisingrecurring units having a carboxyl group which is substituted with anacid labile group having formula (1), an optional acid generator, and anorganic solvent, prebaking the composition to form a resist film,forming a protective film on the resist film, exposing the resist filmto high-energy radiation, baking, and applying an organic solvent-baseddeveloper to dissolve away the protective film and the unexposed regionof resist film for forming a negative pattern wherein the exposed regionof resist film is not dissolved.
 18. A pattern forming process accordingto claim 7, comprising the steps of: applying a resist composition ontoa substrate, the resist composition comprising a polymer comprisingrecurring units having a carboxyl group which is substituted with anacid labile group having formula (1), an optional acid generator, and anorganic solvent, prebaking the composition to form a resist film,forming a protective film on the resist film, exposing the resist filmto high-energy radiation, baking, and applying an organic solvent-baseddeveloper to dissolve away the protective film and the unexposed regionof resist film for forming a negative pattern wherein the exposed regionof resist film is not dissolved.